The present invention relates to lamp sockets, and more particularly to lamp sockets which can be readily connected to current carrying wires to be placed in a set, for example, for use in light strings for tree or outdoor lights, and which have electrical contact members in the socket shell, to engage complementary electrical contact portions of the base of a light bulb within the socket.
In the past, sockets for receiving light bulbs for tree lighting sets have generally included a relatively cylindrical shell having an open end for accommodating the base of a light bulb which is threadably engaged or engaged by a force fit with the socket shell at its inner face. The bottom of the shell is generally provided with an opening through which a pair of insulated current carrying wires passes. A pair of electrical contact members, each having a barb or prong at the lower end, is located on the inside of the shell and a cover member for the base is engaged with the shell base. The cover member is generally designed to force the wire into the shell so that the barb or prong of each electrical contact member engages one of the current carrying wires. A socket which incorporates these features is disclosed in U.S. Pat. No. 3,372,362 assigned to the assignee of the subject application.
In such a socket, one of the two electrical contact members usually has a tab portion which projects across the interior of the socket and is engaged by the bottom contact of the lamp base as the lamp is inserted into the shell. A problem sometimes arises in that with repeated insertions and removals of the lamp from the socket, particularly where the lamp socket is oversize in length, the projecting portion of the contact becomes permanently downwardly deformed and makes poor or no contact with the bottom contact of the lamp base.
In the past, efforts have been made to limit the downward travel of a bulb within the socket to a narrow range to prevent the base of the bulb from deforming the projecting tab portion of the one electrical contact member. The efforts to solve the problem have included providing stop pieces on the inner wall of the shell to prevent insertion of the light bulb base to too great a depth and molding internal threads onto the inner wall of the socket shell for receiving the external threads of a light bulb base. The internal threads have a termination point so disposed as to prevent the external threads of the light bulb base from being threaded too far into the shell.
Neither of these alternatives has been able to accommodate for the range of depths to which the base of a light bulb can extend due to manufacturing tolerances in the production of the bulbs. At present each bulb may extent to a depth slightly greater or lesser than the average. In addition, a person may use excessive force in threading a bulb into the socket. If the bulb extends too far, the projecting portion of the contact will become deformed after repeated insertion.